This invention relates to installation of bushings in a bore, and more particularly to a method and apparatus for installing two spaced bushings concentrically in the two ends of a bore, coaxially with each other.
In the aerospace and other industries, there has long been a requirement for the mounting of bushings in bores in parts, usually to support a shaft which is mounted in the part for supporting or connection to some other part. An example is a flap assembly which requires the installation of pintel pins. The pintel pins must be installed in the bushings in a clevis flap assembly with a very close tolerance sliding fit, and if the bushings are not concentric in the bore and coaxial with each other, the installation of the pins will be difficult or impossible and require extensive and expensive rework on the part in order to be able to install the pintel pins.
The conventional method of installing bushings in such parts is with the use of a press. The part is positioned on the press platen and spacers are positioned to support the part against deflection when the ram of the press is actuated to press the bushing into the bore. A bushing is positioned at the end of the bore and the part is aligned under the ram of the press, then the press is operated to drive the ram down and press the bushing into the bore.
This system works best when jigs and fixtures are available for positioning the part in the press and aligning the bore and bushing with the press ram. However, in many manufacturing plants where bushings are used, the cost of manufacturing jigs and fixtures for each of the numerous parts that have bushings installed becomes very expensive, especially since each bushing in the part must have a different installation fixture and every revision of the part would usually require a redesign of the fixture. More importantly however, even with the use of jigs and fixtures, the conventional process is imperfect because of the impossibility of maintaining alignment of the bushings with the bore and each other while exerting a pressing force on the bushing during installation which is exactly parallel to the axis of the bore.
When the axis of the bushing is misaligned with the axis of the bore or the direction of force exerted on the bushing during installation, or if the pressing surfaces are nonperpendicular to the axis of the bore, the bushing will not be pressed straight into the bore, but will be cocked slightly and gouge the walls of the bore as it is pressed into the bore, and will be pressed into a slightly skewed position in the bore so that it is nonconcentric with the bore and not coaxial with the other bushing inserted at the other end of the bore. This nonconcentricity and/or noncoaxial orientation prevents or makes difficult the proper installation of the pin, shaft, or bolt through the two bushings, requiring removal of the bushings, reboring of the bore in the part, and reinstallation of oversized bushings in the new bore. This rework adds considerably to the cost of the part and slows the production speed of the manufacturing operation.
One of the principle reasons for using bushings in a bore is that they can be replaced when the bushing becomes worn. This makes it possible to replace only the portion of the part which is worn instead of the entire part, which could be very expensive. However, the replacement of bushings is considerably more difficult in the field than it is in the factory. In the field, the bushings are forced into the bore with whatever tools are at hand, including hammers making correct alignment of the bushings in the bore and with each other unusual and primarily a matter of good luck. Another technique in wide use is to insert a bolt through the bushings and the bore, and tighten a nut on the bolt to force the bushings into the bore. This is preferable to pounding the bushings in with a hammer, but is slow and does not ensure either concentricity or coaxial alignment because there is no guidance for the bushings and nothing to keep the bolt coaxially aligned in the bore.
Various other schemes have been devised to solve this problem, but none of these schemes provides the desirable attributes of low cost, simplicity, speed of operation and flexibility of use with numerous different parts. Thus, there has been a long unfulfilled need in the industry for a simple, reliable, inexpensive and flexible process and apparatus for installing bushings concentrically in a bore in which the bushings are held in exact coaxially alignment with each another during installation so that the installed bushings are properly oriented in the bore and to each other.